import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

/**
 * 服务器网络编程
 */
public class UdpEchoServer {
    private DatagramSocket socket = null;
    // 参数是服务器要绑定的端⼝
    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }
    // 使⽤这个⽅法启动服务器.
    public void start() throws IOException {
        System.out.println("服务器启动!");
        while (true) {
            //1.读取请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);//获取二进制报头
            //将报头转为String
            String request = new String(requestPacket.getData(),0,requestPacket.getLength());
            //2.根据请求计算回应
            String response = process(request);
            //3.把响应写回到客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),0,response.getBytes().length);
            socket.send(responsePacket);System.out.printf("[%s:%d] req: %s, resp: %s\n", requestPacket.getAddress(),responsePacket.getPort(), request,response);

        }
    }
    //回显
    private String process(String request) {
        return request;
    }
    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}